adding empty string as default value for forms.
creating browser-based regression tests.  cleaning up form-based errors--one form used a non-standard / different error class.
Merge branch 'develop' of github.com:learningequality/ka-lite into error_on_empty_form_fields
making tests DRYer, reorganizing into proper apps
Fix for issue #290.

*All groups now sent from server to client.
*Tabular view now updates URL correctly from change in Facility or Group
dropdown.
*Selectors now spawned in template for every facility. Only active facility
group selector is shown.
PEP-8 Linting on coachreports views.py
Merge branch 'develop' of github.com:learningequality/ka-lite into change_facility
Consistency fix: Student contexts not returning correct group object.
Coachreports:
Removal of cruft from d3 template that has been abstracted into base.html.
Removed PEP-8 induced line length changes.
Added comments.
Fixed bug that would cause group not to be changed upon facility change in tabular report view.
Made HTML class and id names more meaningful.
Comment explaining JS regex in coach report link changing.
Fix for persistence of URL induced group selection.
Merge pull request #321 from rtibbles/change_facility

Allow change facility and group on both tabular and graph coach reports.
Merge pull request #309 from bcipolli/error_on_empty_form_fields

Error on empty form fields